Brian, the main character in the book "Hatchet," knew a little about how to fly the plane for two reasons.
Firstly, before the plane crash, Brian's mother was dating a man who was a pilot. Brian had spent some time with him and observed him flying the plane. Although he never actually flew the plane himself, he picked up some knowledge and understanding of the basics of flying.
Secondly, during the plane crash, Brian found a survival pack with a transmitter. He managed to turn it on and heard the pilot's voice instructing him on how to fly the plane. Although he didn't fully comprehend everything, he was able to grasp some essential information that helped him control the aircraft to some extent.